Can I give Priority to Some users?

About 40users who conect through the Captive portal. The 4 main users have MAC address Authenticantion the rest usrename & passwords.
All users have been given static IP's and all connect through the same LAN

WAN–pfsense--LAN

I would like to know if I can give priority to 4 (IP's between ...10 - ...19) of the users & split the rest of the bandwidth equally between the others. (IP's ...20 - ...100)??

I have a 512KB Download 128KB upload ADSL line.

If this is possible please could I be informed as to how or pointed in the right direction as to where I may find out how?

The easiest thing to do is run the trafficshaper wizard and enter the alias when it asks you if you want to give priority to voip (unless you run voipapplications). This will put all IPs of that alias into a very high serviceclass.